Winter:Yellowstone is frozen solid – locked in snow as deep as a house for over six months. As we follow the grip of winter over the course of six freezing months, we chart the fortunes of Yellowstone’s wildlife in a finely balanced fight to survive. Bison use their massively powerful heads to dig with through some of the deepest snow in America to reach the grass beneath. A red fox listens out for mice scurrying six feet beneath the snow before diving head first into the drift to snap up its prey, while otters slide through Yellowstone’s winter wonderland to find any remaining open water where they can fish. All the while, as the herds of elk and bison are gradually weakened by the cold, one animal gets stronger – the wolf. But with one of the world’s largest volcanoes beneath the surface, everything from the freezing cold to the creation of a snow storm is determined by the power at Yellowstone’s heart.

Summer:As the spring melts the winter snow, the full extent of Yellowstone is gradually revealed. Now, from the surrounding lowlands herds of elk, pronghorn and bison return from their winter feeding grounds to take advantage of America’s richest natural grasslands – right in the heart of Yellowstone. In only a few weeks, a brutally harsh deep freeze has been transformed into a flower-decked nursery perfect for the year’s newborn animals. There is also a new cast of characters that emerge bleary-eyed from hibernation as grizzly bears begin to teach their young the secrets of survival in Yellowstone – how to hunt fish in the still-frozen rivers and, as the season progresses, when to move out through valleys and grasslands into summer forests and up into Yellowstone’s alpine peaks. In this spectacular wilderness, over 10,000ft high, they slide and scrabble, hunting millions of tiny moths buried under rocks on the barren slopes.But summer here is fickle, even on Midsummer’s Day, winter can descend from the surrounding mountains bringing punishing snows to fragile flower meadows. August is the only month in the year when it does not snow, but then, just as it seems the easy living of summer has finally arrived, it is brought to an abrupt end as fires sweep through the forest, laying Yellowstone to waste.

Autumn:Over the summer, Yellowstone has flourished – in late August there are more living things here than at any other time of the year. But winter is around the corner and there are just two months for all Yellowstone’s animals to get ready or get out.An early dusting of snow is a sign for elk to start moving down from the mountains to focus on finding food in the valleys. Although the wolves are waiting for them, the male elk are distracted, their haunting bugle call boasting that they are fired up and ready to fight each other to the death for the right to breed.As temperatures fall further, beavers get busy in a rush to repair dams and stock underwater larders before ice freezes their ponds. Yellowstone’s forests, the aspens, cottonwoods and maples, start to shut down for the winter, their colours painting Yellowstone a blaze of red and gold. Meanwhile another tree is coming into its own, the whitebark pine. It offers up a bumper crop of pine nuts which fatten grizzly bears and squirrels alike. But its nuts are meant for another animal – the Clark’s nutcracker – a small bird with a colossal memory, and one that will reward the tree’s efforts well by carrying its seeds far and wide and even planting them.As autumn ends, the snow and ice return and many animals now move out from the heart of Yellowstone and so away from the protection of the national park. Here, their fight is not only to survive the cold, but also to find what little wild space remains in the modern world. All around Yellowstone, the human world is encroaching – it is now that the true value of the ‘world’s first national park’ becomes clearer than ever.